Sealing device

ABSTRACT

A sealing device in which a good lubricating oil film is formed along the entire circumference of a sliding surface. The sealing device ( 1 ) is fitted in an annular groove formed in either of two elements that are a housing having a shaft hole and a shaft inserted through the shaft hole, and the sealing device ( 1 ) seals an annular gap between the two elements. The sealing device ( 1 ) has a seal ring ( 2 ) sliding against the other element by relative axial movements of the two elements. In the seal ring ( 2 ), on each of axially opposite ends of a sliding surface ( 20 ) sliding against the other element, there are formed grooves ( 22 ) extending from an end surface ( 21 ) of the seal ring ( 2 ) toward the axial center of a sliding surface ( 20 ). Further, in the seal ring ( 2 ), the boundary between each groove ( 22 ) and the sliding surface ( 20 ) is formed only by lines inclined relative to the direction of sliding of the sliding surface ( 20 ), and grooves ( 23 ) are circumferentially adjacently arranged in the seal ring ( 2 ) so that regions each having the boundary formed by the inclined lines are continuous along the entire circumference of the sliding surface ( 20 ).

TECHNICAL FIELD

The present invention relates to a sealing device used for a hydrauliccylinder or the like.

BACKGROUND ART

Conventionally, a sealing device shown in FIG. 15 is used between ahydraulic cylinder and a piston. FIG. 15 is a schematic half sectionalview of the prior-art sealing device.

The sealing device 100 is for sealing an annular gap 400 between aninner peripheral face 201 of the cylinder 200 and an outer peripheralface 301 of the piston 300 and is fitted in an annular groove 302 formedin the outer peripheral face 301 of the piston 300. The sealing device100 is formed of a resin seal ring 101 for sliding against the innerperipheral face 201 of the cylinder 200 and an elastic ring 102 fittedbetween the seal ring 101 and a groove bottom 303 of the annular groove302 to give enlarging force to the seal ring 101.

In such a sealing device, an oil film made of lubricating oil is formedon a sliding surface between the seal ring 101 and the inner peripheralface 201 of the cylinder 200, which suppresses wearing and slidingresistance of the sliding surface and prevents occurrence of an unusualnoise, stick slip, production of heat, and the like.

Provision of grooves in order to introduce the lubricating oil into thesliding surface of the seal ring to more reliably form the lubricatingfilm or to maintain the lubricating film for a longer period of time isdescribed in Patent Documents 1 and 2, for example.

Patent Document 1: Japanese Patent Application Laid-Open No. 2001-304413

Patent Document 2: Japanese Utility Model Application Laid-Open No.07-043672

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In the technique described in the Patent Document 1, however, groovesconnecting a side to be sealed and an opposite side to the side to besealed are formed in a sliding surface between a cylinder innerperipheral face and a bearing member surface and therefore the techniquecannot be applied to a position that requires sealing.

Although grooves in a sliding surface are formed so as not to connect aside to be sealed and an opposite side to the side to be sealed in thetechnique described in the Patent Document 2, a lubricating film formedby the grooves does not cover the entire circumference of the slidingsurface and sufficient effect cannot be obtained in some cases.

The present invention has been made to solve the above problems in theprior art and it is an object of the invention to provide a sealingdevice for forming a preferable lubricating film along the entirecircumference of a sliding surface.

Means for Solving the Problems

To achieve the above object, there is provided a sealing device mountedin an annular groove formed in one of two members that are a housinghaving a shaft hole and a shaft inserted into the shaft hole to seal anannular gap between the two members, the device including a seal ringfor sliding against the other member due to relative axial movements ofthe two members, wherein the seal ring includes, on each of axialopposite end portions of a sliding surface sliding against the othermember, a plurality of grooves extending from an end face of the sealring toward an axial center of the sliding surface, a boundary betweenthe grooves and the sliding surface is formed only of lines inclinedwith respect to a sliding direction of the sliding surface, and theplurality of grooves are arranged to be adjacent to each other in acircumferential direction so that an area in which the boundary isformed of the inclined lines continues along an entire circumference ofthe sliding surface.

By forming the boundary between the grooves and the sliding surface onlyof the lines inclined with respect to the sliding direction, lubricatingoil introduced into the grooves diagonally enter edge portions of thesliding surface due to the relative movements of the two members. As aresult, resistance to entry of the lubricating oil into the slidingsurface is reduced and a preferable lubricating film can be formed.

Here, surface pressure generated on the sliding surface is the highestat the end portions of the sliding surface and a surface pressuredistribution shape has steep slopes at the end portions of the slidingsurface where the surface pressure abruptly increases inward from theedge portions. Therefore, the lubricating oil that enters in a directionorthogonal to the edge portion of the sliding surface receives such aresistance that it has to climb the steep slope straight. On the otherhand, if the lubricating oil diagonally enters the edge portion of thesliding surface, the lubricating oil receives such a resistance that itdiagonally climbs the steep slope, i.e., gently climbs the slope, whichreduces the resistance to entry of the lubricating oil into the slidingsurface.

Therefore, it is easy to send more lubricating oil to the slidingsurface and it is possible to form a thicker lubricating film.

Moreover, because the area in which the lubricating oil introduced intothe grooves diagonally enters the edge portions of the sliding surfacecontinues along the circumferential direction, the resistance to entryof the lubricating oil is reduced along the entire circumference of thesliding surface. Therefore, it is possible to form the preferablelubricating film along the entire sliding surface.

The sliding surface may include a recessed portion between the groovesformed at one end portion and the grooves formed at the other endportion.

By providing the recessed portion, it is possible to efficiently form anoil film, even if a stroke of relative movements of the two members isshort. In other words, the lubricating oil that has reached the recessedportion from the grooves at the one end portion with the first stroke istemporarily retained in the recessed portion and moves farther towardthe other end portion with the second stroke. In this way, it ispossible to cover the sliding surface from one side to the other sidewith the oil film, even if the stroke is short.

The grooves may be inclined grooves extending to be inclined withrespect to the axial direction and one and the other of the inclinedgrooves adjacent to each other in the circumferential direction may beadjacent to each other in such a manner that an overlap is formedbetween them when viewed in the axial direction.

If the grooves are the inclined grooves, the lubricating oil candiagonally enter the edge portions of the sliding surface.

If the grooves adjacent to each other in the circumferential directionpartially overlap each other in the circumferential direction, the areain which the lubricating oil introduced into the grooves diagonallyenters the edge portions of the sliding surface continues in thecircumferential direction. As a result, the resistance to entry of thelubricating oil is reduced along the entire circumference of the slidingsurface and it is possible to form the preferable lubricating film alongthe entire sliding surface.

The grooves may be wedge-shaped grooves and provided continuously alongthe entire circumference of the sliding surface.

If the grooves are the wedge-shaped grooves, the lubricating oil candiagonally enter the edge portions of the sliding surface. Because thelubricating oil introduced into the groove is gradually pushed into thenarrower space, surface pressure on the sliding surface can be reducedby a wedge effect.

By continuously providing the wedge-shaped grooves, the edge portions ofthe sliding surface are in a serrated shape. Therefore, the lubricatingoil diagonally enters the edge portions of the sliding surface along theentire circumference of the sliding surface. As a result, the resistanceto entry of the lubricating oil is reduced along the entire slidingsurface and it is possible to form a preferable lubricating film.

It is preferable that an axial width of the sliding surface does notchange along the entire circumference.

As a result, a sliding width of the seal ring is constant in thecircumferential direction and volume of a section is uniform in thecircumferential direction and therefore strength of the seal ring isuniformized and stabilized to thereby suppress occurrence of damage dueto nonuniform strength. Moreover, because the sliding width in the axialdirection is constant in any sections, occurrence of perforating injuryon the sliding surface due to a foreign matter is suppressed and sealingperformance is stabilized.

Effect of the Invention

As described above, with the invention, it is possible to form thepreferable lubricating film along the entire circumference of thesliding surface.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1( a) to 1(c) are schematic diagrams showing a structure of asealing device according to an first embodiment.

FIG. 2 is a schematic perspective view of the sealing device accordingto the first embodiment.

FIGS. 3( a) and (b) are schematic half sectional views of a mountedstate of the sealing device according to the first embodiment.

FIG. 4 is a schematic diagram showing a structure of an outer peripheralface of a seal ring of the sealing device according to the firstembodiment.

FIG. 5 is a drawing schematically showing surface pressure distributionformed on a sliding surface of the seal ring.

FIGS. 6( a) to 6(c) are schematic diagrams showing a structure of asealing device according to an second embodiment.

FIG. 7 is a schematic perspective view of the sealing device accordingto the second embodiment.

FIG. 8 is a schematic diagram showing a general structure of a testingmachine.

FIG. 9 is a chart for comparing sliding resistances of seal rings.

FIG. 10 is a chart for comparing achieving temperatures of the sealrings.

FIG. 11 is a chart for explaining a relationship between a pressurereceiving area and the achieving temperature.

FIGS. 12( a) to 12(g) are schematic diagrams showing a structure of asealing device according to a third embodiment.

FIG. 13 is a schematic diagram showing a structure of an outerperipheral face of a seal ring of a sealing device according to a fourthembodiment.

FIGS. 14( a) to 14(c) are schematic half sectional views of sealingdevices according to modifications.

FIG. 15 is a schematic half sectional view of a prior-art sealingdevice.

EXPLANATIONS OF REFERENCE NUMERALS

1 sealing device

2 seal ring

20 outer peripheral face

21 side face

22 groove

23 wedge-shaped groove

24 recessed portion

3 elastic ring

4 housing

40 inner peripheral face

5 shaft

50 annular groove

51 side face

52 groove bottom

6 annular gap

BEST MODES FOR CARRYING OUT THE INVENTION

Best modes for carrying out the present invention will be describedbelow in detail by using examples based on embodiments with reference tothe drawings. However, dimensions, material, shapes, and relativepositions of component parts described in the embodiments are notintended to limit a scope of the invention unless otherwise specified.

First Embodiment

First, with reference to FIGS. 1 to 3, a general structure of a sealingdevice according to the embodiment of the invention will be described.FIGS. 1( a) to 1(c) are schematic diagrams showing a structure of thesealing device according to the embodiment. FIG. 1( a) is a view from anaxial direction, FIG. 1( b) is a sectional view taken along a line A-Ain FIG. 1( a), and FIG. 1( c) is a view from a direction of an arrow Bin FIG. 1( a). FIG. 2 is a schematic perspective view of the sealingdevice according to the embodiment. FIGS. 3( a) and 3(b) are schematichalf sectional views of a mounted state of the sealing device accordingto the embodiment. FIG. 3( a) shows a state without pressure and FIG. 3(b) shows a state under pressure.

The sealing device 1 according to the embodiment is used as a sealingdevice for a piston in a hydraulic cylinder, for example, and is formedof a seal ring 2 and an elastic ring 3. The sealing device 1 is fittedin an annular groove 50 formed in an outer peripheral face of a shaft 5so as to seal an annular gap 6 between a housing (cylinder) 4 having ashaft hole and the shaft (a piston, a rod, or the like) 5 inserted intothe shaft hole.

The seal ring 2 is an annular member having a substantially rectangularsection and disposed on a side of an opening portion of the annulargroove 50. An outer peripheral face 20 of the seal ring 2 slides againstan inner peripheral face 40 of the housing 4 to thereby form a seal facefor the housing 4. When oil pressure OP is applied, the seal ring 2 ispushed against an opposite side of the annular groove 50 to the oilpressure. As a result, a side face (end face) 21 of the seal ring 2 onthe opposite side to the oil pressure comes in close contact with a sideface 51 of the annular groove 50 to thereby form a seal face for theshaft 5.

As material of the seal ring 2, it is possible to usepolytetrafluoroethylene (PTFE) widely used for a sliding member ingeneral and all the general-purpose thermoplastic engineering resinssuch as polyamide (PA), polyether ether ketone (PEEK), polyphenylenesulfide (PPS), and polyacetal (POM).

The elastic ring 3 is an annular member having a substantially circularsection and made of rubber material such as nitrile rubber and iscompressed and fitted between the seal ring 2 and a groove bottom 52 ofthe annular groove 50. The elastic ring 3 biases the seal ring 2 towardthe housing 4 with its elastic resilience to increase adhesion betweenthe seal ring 2 and the housing 4. The sectional shape of the elasticring 3 is not limited to the circle and various shapes can be employedproperly.

A plurality of grooves 22 are formed in the outer peripheral face 20 ofthe seal ring 2 that is a sliding surface against the inner peripheralface 40 of the housing 4. The grooves 22 are inclined grooves extendingfrom the side faces 21 of the seal ring 2 toward an inside (a center inan axial direction) of the outer peripheral face 20. The grooves 22 arerespectively formed on axial opposite sides (opposite end portions) ofthe outer peripheral face 20 and have depths extending radially from theend portions of the outer peripheral face 20 to stop before a centralportion.

Next, with reference to FIGS. 4 and 5, the grooves 22 formed in theouter peripheral face 20 and characterizing the sealing device 1according to the embodiment will be described in detail. FIG. 4 is aschematic diagram showing a structure of the outer peripheral face 20 ofthe seal ring 2 of the sealing device 1 according to the embodiment.FIG. 5 is a drawing schematically showing surface pressure distributionformed on the sliding surface of the seal ring. The grooves 22 havesimilar structures and are symmetrically formed in the axial directionon the opposite end portions of the outer peripheral face 20. Therefore,only the grooves on one of the end portions will be described in thefollowing description and the grooves on the other end portion will notbe described.

The grooves 22 are formed to facilitate interposition of lubricating oilin a sliding portion between the inner peripheral face 40 of the housing4 and the outer peripheral face 20 of the seal ring 2 and extend fromthe side face 21 of the seal ring 2 toward the center side of the outerperipheral face 20 in directions inclined with respect to the axialdirection.

All boundaries between the grooves 22 and the outer peripheral face 20,i.e., edge portions 20 a, 20 b, and 20 c of the outer peripheral face 20at portions provided with the grooves 22 are formed of lines inclinedwith respect to the axial direction (sliding direction C of the sealring 2) and therefore the lubricating oil introduced into the grooves 22diagonally enter the edge portions 20 a, 20 b, and 20 c of the outerperipheral face 20 (arrows D) due to sliding of the seal ring 2. In thisway, resistance to entry of the lubricating oil into the outerperipheral face 20 is reduced and it is possible to satisfactorily forma lubricating film.

In other words, the surface pressure generated on the sliding surface(outer peripheral face) of the seal ring S is the highest at theopposite end portions (end faces S2) of the sliding surface S1 and thesurface pressure distribution shape P has steep slopes P1 at the endportions of the sliding surface S1 where the surface pressure abruptlyincreases from edges to maximum surface pressure Pmax.

Therefore, if the edge portion S3 of the sliding surface S1 isorthogonal to the sliding direction (an arrow E) of the seal ring S, thelubricating oil enters the edge portion 53 of the sliding surface S1 inan orthogonal direction to the edge portion S3 and receives such aresistance that it has to climb the steep slope P1 straight (an arrowF).

On the other hand, if the lubricating oil diagonally enters the edgeportion S3 of the sliding surface S, the lubricating oil receives such aresistance that it diagonally climbs the steep slope P1 (an arrow G),i.e., gently climbs the slope P1, which reduces the resistance to entryof the lubricating oil into the sliding surface.

Therefore, as shown in FIG. 4, with such a structure that thelubricating oil introduced into the groove 22 enters the outerperipheral face (sliding surface) 20 not in orthogonal directions but indiagonal directions to the edge portions 20 a, 20 b, and 20 c, theresistance to entry of the lubricating oil can be reduced and it is easyto send more lubricating oil to the outer peripheral face 20. As aresult, it is possible to interpose a thick lubricating film between theinner peripheral face 40 of the housing 4 and the outer peripheral face20 of the seal ring 2.

Moreover, an overlap H in a circumferential direction is formed betweena groove 22 a and a groove 22 b adjacent to each other in thecircumferential direction. In other words, the groove 22 a and thegroove 22 b are adjacent to each other in such a manner that the closestportion of the groove 22 a to the groove 22 b (an entrance portion ofthe groove 22 a) and the closest portion of the groove 22 b to thegroove 22 a (an inner portion of the groove 22 b) are arranged in apartially staggered configuration in the circumferential direction. Inother words, on a phantom line extending in the axial direction (slidingdirection) from any one point on the boundary between one 22 a of theadjacent grooves 22 a and 22 b and the outer peripheral face 20, theboundary between the other groove 22 b and the outer peripheral face 20exists. When the grooves 22 a and 22 b are seen from the axial direction(projected), they overlap each other (the overlap H is formed).

By forming the overlap between the adjacent grooves, an area where thelubricating oil introduced into the grooves 22 diagonally enters theedge portions of the outer peripheral face 20 continues along the entirecircumference of the outer peripheral face 20. Therefore, the resistanceto entry of the lubricating oil is reduced along the entirecircumference of the outer peripheral face 20 and it is possible to formthe satisfactory lubricating film along the entire circumference of theouter peripheral face 20.

Second Embodiment

Next, a sealing device according to a second embodiment of the inventionwill be described with reference to FIGS. 6 and 7. FIGS. 6( a) to 6(c)are schematic diagrams showing a structure of the sealing deviceaccording to the embodiment. FIG. 6( a) is a view from the axialdirection, FIG. 6( b) is a sectional view taken along a line I-I in FIG.6( a), and FIG. 6( c) is a view from a direction of an arrow J in FIG.6( a). FIG. 7 is a schematic perspective view of the sealing deviceaccording to the embodiment. Components similar to those in the firstembodiment will be provided with same reference numerals and descriptionof them will not be repeated while only different points will bedescribed.

In the sealing device 1′ according to the embodiment, grooves formed inthe outer peripheral face 20 of the seal ring 2 are wedge-shaped grooves23. In other words, a groove width of the wedge-shaped groove 23gradually reduces from the side face 21 of the seal ring 2 toward theinside (the axial center) of the outer peripheral face 20 and a depth ofthe groove 23 extends radially from the end portion of the outerperipheral face 20 and stops before a central portion.

As shown in FIGS. 6( a) to 7, the adjacent wedge-shaped grooves 23 areprovided continuously without intervals in the circumferential directionand a boundary between the wedge-shaped grooves 23 and the outerperipheral face 20, i.e., edge portions of the outer peripheral face 20are in a serrated shape. Therefore, the edge portions of the outerperipheral face 20 are formed only of diagonal lines with respect to theaxial direction (sliding direction of the seal ring 2) and theresistance to entry of the lubricating oil is reduced along the entirecircumference of the outer peripheral face.

Because the lubricating oil is pushed into the space formed of thewedge-shaped groove 23 and gradually narrowing in the siding direction,forces for moving the housing 4 and the seal ring 2 away from each otherare generated and the surface pressure between the inner peripheral face40 of the housing 4 and the outer peripheral face 20 of the seal ring 2is reduced (a wedge effect). As a result, a surface pressure gradient ofthe outer peripheral face 20 of the seal ring 2 is reduced and it ispossible to interpose an appropriate lubricating film between thehousing 4 and the seal ring 2.

Here, the wedge effect exerted by the wedge-shaped groove 23 increasesas an angle formed by the two boundaries between the respectivewedge-shaped grooves 23 and the outer peripheral face 20 form becomessmaller, i.e., as a tip end angle of the wedge shape of the wedge-shapedgroove 23 becomes more acute, which increases the effect of reduction inthe surface pressure gradient.

If an area of the outer peripheral face 20 is small, i.e., if a contactarea with the inner peripheral face 40 of the housing 4 is small, thesurface pressure becomes high. Therefore, an axial depth (length) of thewedge-shaped groove 23 is preferably shallow (short) so as not to reducethe area of the outer peripheral face 20 beyond necessity.

(Verification of Lubrication Improvement Effect)

Here, the effect of improving the lubrication characteristic in thesecond embodiment was verified with reference to FIGS. 8 to 11 based onresults of tests comparing with prior-art products. FIG. 8 is aschematic diagram showing a general structure of a testing machine. FIG.9 is a chart for comparing sliding resistances of seal rings. FIG. 10 isa chart for comparing achieving temperatures of the seal rings. FIG. 11is a chart for explaining a relationship between a pressure receivingarea and the achieving temperature.

As shown in FIG. 8, the testing machine includes a cylinder 4 a and apiston 5 a coupled to a driving cylinder (not shown) to axiallyreciprocate in the cylinder 4 a. In annular grooves formed in oppositeends of an outer peripheral face of the piston 5 a, seal rings 2 a and 2b as samples to be evaluated are fitted, respectively. A wear ring 7 ismounted between the two samples and pressure passing through a hose 8and an inside of the piston 5 a is applied between the two samples. Areference numeral 9 designates a load cell and 10 designates a walltemperature measuring portion for measuring wall temperature of thecylinder 4 a.

While predetermined constant pressure (10 MPa, 30 MPa, or the like) wasapplied between the two samples and the pressure was acting on thesealing devices 2 a and 2 b, the piston 5 a was reciprocated by thedriving cylinder and the sealing devices 2 a and 2 b were slid againstthe inner peripheral face of the cylinder 4 a.

When the wall temperature of the cylinder 4 a increases due toproduction of heat caused by reciprocation of the piston 5 a and thetemperature increase becomes saturated, temperature at this time(temperature when heat production and heat radiation become balanced) isdefined as the achieving temperature and the achieving temperature wasmeasured.

The sliding resistance was measured by measuring a load necessary forreciprocation of the piston 5 a with the load cell 9 and extracting thesliding resistance from the waveform.

A product corresponding to the seal ring 2 in the second embodiment,i.e., the product having the wedge-shaped grooves formed continuously onaxial opposite ends of the outer peripheral face (sliding surface) ofthe seal ring was taken as an embodiment product, a prior-art seal ringwithout wedge-shaped grooves and having a rectangular section was takenas a prior-art product 1, a seal ring in which axial opposite ends of aseal ring outer peripheral face were tapered was taken as a prior-artproduct 2, and various values such as achieving temperatures and slidingresistances of them were compared.

As shown in FIG. 9, the sliding resistance of the embodiment product was273 kgf while the sliding resistances of the prior-art product 1 and theprior-art product 2 were 438 kgf and 375 kgf, respectively. In otherwords, by forming the wedge-shaped grooves, the sliding resistance wasreduced by 37% from that of the prior-art product 1 and by 14% from thatof the prior-art product 2. Therefore, it is clear that the slidingresistance of the embodiment product provided with the wedge-shapedgrooves is reduced by a greater amount from that of the prior-artproduct 1 without any grooves than that of the prior-art product 2provided with the tapered faces. Here, the test was conducted underconditions of reciprocation speed of 100 mm/sec, the pressure betweenthe two samples of 30 MPa, and a stroke length of 100 mm. In this test,the testing machine was actuated while constantly maintainingtemperature of an outer peripheral face (outer wall) at a portion asclose as possible to the sliding portion (inner peripheral face) of thecylinder at 100° C. To put it concretely, a hole was formed with a drillby stopping the drill immediately before it penetrated the cylinder fromthe outer periphery side to the inner periphery side (about 1 mm), athermocouple that was a temperature sensor was embedded in the hole,heating was controlled with a heater so that a measured temperature bythe thermocouple was constantly maintained at 100° C. In this way, thetemperature near the sliding surface of the cylinder was constantlymaintained at 100° C.

As shown in FIG. 10, the achieving temperature when the pressure betweenthe two samples was 10 MPa in the embodiment product was 75° C. whilethe achieving temperatures in the prior-art product land the prior-artproduct 2 were 87° C. and 76° C., respectively. The achievingtemperature of the embodiment product was 12° C. lower than that of theprior-art product 1. The achieving temperature when the pressure betweenthe two samples was 30 MPa in the embodiment product was 102° C. whilethe achieving temperature in the prior-art product 1 was 126° C. Theachieving temperature of the embodiment product was 24° C. lower thanthat of the prior-art product 1. In other words, it is clear that theembodiment product is less susceptible to heat produced by sliding thanthe prior-art product 1. Because the reduction rate of the achievingtemperature from that of the prior-art 1 was greater when the pressurewas 30 MPa than when it was 10 MPa, it is clear that the embodimentproduct is suitable especially for use under high pressure. Here, thetest was conducted under conditions of reciprocation speed of 50 mm/secand the stroke length of 100 mm.

As shown in FIG. 11, although the embodiment product has a largercontact area and a larger effective pressure receiving area than theprior-art product 2 and has the smaller reduction rate in the pressurereceiving area from the prior-art product 1 than the prior-art product2, it has the same level of achieving temperature as the prior-artproduct 2. In other words, because the embodiment product has the samelevel of reduction rate in the achieving temperature in spite of thesmaller reduction rate in the pressure receiving area, it is estimatedthat provision of the wedge-shaped grooves as in the embodiment producthas greater lubrication improvement effect than provision of the taperedfaces as in the prior-art product 2.

Third Embodiment

Next, with reference to FIG. 12, a sealing device according to a threeembodiment of the invention will be described. FIGS. 12( a) to 12(g) aredrawings for explaining differences between structures of the sealingdevice according to the present embodiment and the sealing deviceaccording to the second embodiment. FIG. 12( a) is a schematic diagramshowing the sectional structure of the sealing device according to thesecond embodiment and the structure of the outer peripheral face of theseal ring, FIG. 12( b) is a sectional view taken along a line K-K inFIG. 12( a), FIG. 12( c) is a sectional view taken along a line L-L inFIG. 12( a), FIG. 12( d) is a schematic diagram showing a sectionalstructure of the sealing device according to the three embodiment and astructure of an outer peripheral face of a seal ring, FIG. 12( e) is asectional view taken along a line M-M in FIG. 12( d), FIG. 12( f) is asectional view taken along a line N-N in FIG. 12( d), and FIG. 12( g) isa sectional view taken along a line O-O in FIG. 12( d). The sectionsdescribed here are sections along planes including an axis of thesealing device and the same holds true for sections in the followingdescription.

As shown in FIG. 12( a), in the wedge-shaped grooves 23 formed on theouter peripheral face of the seal ring 2 of the sealing device accordingto the second embodiment, wedge-shaped grooves 23 a formed on one sidein the axial direction of the outer peripheral face 20 and wedge-shapedgrooves 23 b formed on the other side are disposed symmetrically in theaxial direction, i.e., boundaries between the wedge-shaped groovesadjacent to each other in the circumferential direction and apexes ofthe wedge shapes are aligned in the circumferential direction.Therefore, axial width of the sliding surface (outer peripheral face 20)changes in the circumferential direction and volume of the section ofthe seal ring 2 changes in the circumferential direction.

In other words, as shown in FIG. 12( b), in the section along theboundary between the wedge-shaped grooves adjacent in thecircumferential direction, the sliding surface (outer peripheral face20) is formed to cover width of the seal ring 2 (axial length of theouter peripheral face) and sliding width Wa is the largest. The volumeof the section of the seal ring 2 is also the largest at this time. Asshown in FIG. 12( c), in the section at the apex of the wedge shape ofthe wedge-shaped groove, the sliding surface is formed between theapexes of the one wedge-shaped groove 23 a and the other wedge-shapedgroove 23 b and the sliding width Wb is the smallest. The volume of thesection of the seal ring 2 is the smallest at this time.

On the other hand, in the sealing device according to the embodiment, inthe wedge-shaped grooves 23 formed in the outer peripheral face of theseal ring 2, the wedge-shaped grooves 23 a provided on one side in theaxial direction of the outer peripheral face 20 and the wedge-shapedgrooves 23 b provided on the other side are staggered, i.e., apexes ofthe one wedge-shaped grooves are aligned in the circumferentialdirection with boundaries between the other wedge-shaped groovesadjacent to each other. Therefore, as shown in FIG. 12( d), the slidingsurface is meandering in the circumferential direction in theembodiment. As shown in FIGS. 12( e) to 12(g), axial width Wc of thesliding surface is always constant. Moreover, volume of the section ofthe seal ring 2 is also constant in the circumferential direction.

In the embodiment, because the sliding width Wc of the seal ring 2 isconstant in the circumferential direction and the volume of the sectionis uniform without changing in the circumferential direction, strengthof the seal ring 2 is uniformized and stabilized to thereby suppressoccurrence of damage due to nonuniform strength. Moreover, because thesliding width Wc in the axial direction is constant in any sections,occurrence of perforating injury on the sliding surface due to a foreignmatter is suppressed and sealing performance is stabilized.

Fourth Embodiment

Next, a sealing device according to a fourth embodiment of the inventionwill be described with reference to FIG. 13. FIG. 13 is a schematicdiagram showing a structure of an outer peripheral face of a seal ringof the sealing device according to the embodiment. Components similar tothose in the above embodiments will be provided with same referencenumerals and description of them will not be repeated while onlydifferent points will be described.

The sealing device 1″ according to the embodiment is the sealing device1 according to the embodiment, but with the seal ring 2 having recessedportions 24 formed in an area between the grooves 22 formed at the oneend portion of the outer peripheral face 20 and the grooves 22 formed atthe other end portions.

By forming the recessed portions 24 in this manner, it is possible toefficiently form an oil film, even if a stroke of relative movements ofthe housing 4 and the shaft 5 in the axial direction is short. In otherwords, the lubricating oil that has reached the recessed portions 24from the grooves 22 at the one end portion with the first stroke istemporarily retained in the recessed portions 24 and moves farther (tothe other end portion) with the second stroke. In this way, it ispossible to cover the outer peripheral face 20 from one side to theother side with the oil film, even if the stroke is short.

If the recessed portions 24 are applied to the sealing devices of eachof the above embodiments, the similar effect can be obtained.

Although the sealing device according to each of the embodiments ismounted in the mounting groove formed in the outer periphery of theshaft in the above description, the invention is not limited to it. Itis also possible that the sealing device is mounted in a mounting grooveformed in the shaft hole of the housing to slide against the outerperipheral face of the shaft.

With the sealing device according to each of the embodiments, thelubrication performance on the sliding surface is improved as describedabove, which expands a range of options of a material of the seal ring.In other words, it is possible to employ, as material of the seal ring2, general-purpose engineering resins such as polyamide (hereafterreferred to as PA) which has not been basically employed for theconventional sliding member.

As compared with polytetrafluoroethylene (hereafter referred to as PTFE)which is excellent in sliding characteristic and used most widely, PAand the like are inferior in the sliding characteristic but lower in aunit price of a raw material allows lower material cost of the sealling.

If PTFE is employed for use under high pressure, it is necessary to usea backup ring made of PA or the like as well to prevent the seal ring 20from protruding into the annular gap 6. On the other hand, PA or thelike with higher elasticity than PTEF has functions of both the sealring and backup ring and therefore can be used alone without the backupring even for the use under high pressure, which reduces the number ofmembers.

From the view point of production, PTFE needs to be formed into materialby compression molding and the material needs to be formed into a finalshape by cutting or the like. PA or the like, on the other hand, can bemass produced in the small number of steps by injection molding.Therefore, the number of production steps can be reduced and productioncost can be reduced substantially due to the above-mentioned lowermaterial cost.

(Modifications)

Sealing devices according to modifications of the invention will bedescribed with reference to FIGS. 14( a) to 14(c). FIGS. 14( a) to 14(c)are schematic half sectional views of structures of the sealing devicesaccording to the various modifications of the invention.

Although each of the above embodiments employs a structure combining theseal ring having the substantially rectangular section and the elasticring having the circular section as the structure of the sealing device,the invention is not limited to such a structure. Therefore, as thestructure of the sealing device, it is also possible to employ astructure in combination with what is called a rectangular ring 3 ahaving a rectangular section as shown in FIG. 14( a) or what is called aD ring 3 b having a substantially D-shaped section as shown in FIG. 14(b) as a biasing member for the seal ring, for example.

Moreover, as shown in FIG. 14( c), it is also possible to employ astructure combining an elastic ring 3 c having a substantially T-shapedodd-shaped section and backup rings 7 respectively disposed on axialopposite sides of the seal ring 2 and the elastic ring 3 c to preventprotrusion of the seal ring 2 into the annular gap.

A scope of application of the invention is not limited to use of it asthe sealing device for reciprocation as in each of the aboveembodiments. It is needless to say that similar effects to those in theabove embodiments can be obtained if the invention is applied to a resinwear ring, a metal bearing, or the like for reciprocation, for example.

1. A sealing device mounted in an annular groove formed in one of twomembers that are a housing having a shaft hole and a shaft inserted intothe shaft hole to seal an annular gap between the two members, thedevice comprising a seal ring for sliding against the other member dueto relative axial movements of the two members, wherein the seal ringincludes, on each of axial opposite end portions of a sliding surfacesliding against the other member, a plurality of grooves extending froman end face of the seal ring toward an axial center of the slidingsurface, a boundary between the grooves and the sliding surface isformed only of lines inclined with respect to a sliding direction of thesliding surface, and the plurality of grooves are arranged to beadjacent to each other in a circumferential direction so that an area inwhich the boundary is formed of the inclined lines continues along anentire circumference of the sliding surface.
 2. The sealing deviceaccording to claim 1, wherein the sliding surface includes a recessedportion between the grooves formed at one end portion and the groovesformed at the other end portion.
 3. The sealing device according toclaim 1, wherein the grooves are inclined grooves extending to beinclined with respect to the axial direction and one and the other ofthe inclined grooves adjacent to each other in the circumferentialdirection are adjacent to each other in such a manner that an overlap isformed between them when viewed in the axial direction.
 4. The sealingdevice according to claim 1, wherein the grooves are wedge-shapedgrooves and provided continuously along the entire circumference of thesliding surface.
 5. The sealing device according to claim 4, wherein anaxial width of the sliding surface does not change along the entirecircumference.
 6. The sealing device according to claim 2, wherein thegrooves are inclined grooves extending to be inclined with respect tothe axial direction and one and the other of the inclined groovesadjacent to each other in the circumferential direction are adjacent toeach other in such a manner that an overlap is formed between them whenviewed in the axial direction.
 7. The sealing device according to claim2, wherein the grooves are wedge-shaped grooves and providedcontinuously along the entire circumference of the sliding surface.